AHJ buying off conductors in conduit, at 42% fill?

As far as the inspector, I'm in line with post #15 in that, it being a 4" conduit, I doubt the inspector is going to check it, but in regard to the ".003%" you stated that was without an EGC. Add the EGC and using Cu with two 90s the electricians are more likely to have the problem.
 
The numbers that were ran were calculated but used generic conductor diameters based on comp and insulation, so far anyway. I've not talked to the AHJ because I'm not sure I want to walk that road and hold a big red flag in the air. Usually with a professional printed procedural document, they usually accept the competence part, and just inspect that it's hooked up...

When numbers are evaluated using 6, 500s, reduced neutral, and proper copper EGC, I can get it to right at 40% if that really needs pushed. It then becomes a decision on how much 277 is really desired or needed. This is a remod so this is not about load matching, it's about maxing out that pipe with wire to future proof the build. My preference is more pipes but I doubt that will happen. Actually I think they will prefer our other method of 4, 750 coppers and be done with it.

I am not a fan of pulling big copper. yes, I would end up onsite to both assist and oversee. Aluminum is what I prefer. It's just easier IMO to pull and do a nice job.
 
fastline said:
It then becomes a decision on how much 277 is really desired or needed
Click to expand...
Unless you are intentionally trying to set up a system to overload the neutral there could be nothing but 277V loads and the neutral conductor would still carry loads at a fraction of the ungrounded conductors. I've never seen a reason for a full size neutral other chest thumping in regards to how much better my full size neutral is than those hacks that use a reduced one.
 
ActionDave said:
Unless you are intentionally trying to set up a system to overload the neutral there could be nothing but 277V loads and the neutral conductor would still carry loads at a fraction of the ungrounded conductors. I've never seen a reason for a full size neutral other chest thumping in regards to how much better my full size neutral is than those hacks that use a reduced one.
Click to expand...
It was a first and initial calc as sometimes we do it just so we can say we did. The days of power hog lighting are over. What I see now is some 240 1P loads off 277 with a buck/boost. No complaints here, just saying that having 277 is better than not having 277, which is why I am recommending that neutral pull, even though not one damn thing is running it right now.

I might even run harder numbers to see what compact Al conductors will fit because everyone wants copper until they see the price. I hate pulling it, and they hate paying for it. Nothing wrong with Al. But I STILL get people saying Aluminum is bad and will burn your place down....lol They are stuck in the 70s. Todays alloys are solid.
 
So you hate to spend extra money on a different conductor metal but you don't mind spending money on a full size neutral and possibly overfill a pipe even though that neutral can never carry anything but the imbalance of the ungrounded conductors? What difference does it make if the whole building is full of nothing but old school "power hog lighting", whatever that is?
 
ActionDave said:
So you hate to spend extra money on a different conductor metal but you don't mind spending money on a full size neutral and possibly overfill a pipe even though that neutral can never carry anything but the imbalance of the ungrounded conductors? What difference does it make if the whole building is full of nothing but old school "power hog lighting", whatever that is?
Click to expand...
I'm NOT the one spending, I just feed the information and calcs to the customer. I'm just super sorry if that somehow hurt your feelings! yes, sometimes neutrals are oversized for no good reason, and I have no idea what "different conductor metal" you speak of. Smells like two standard flavors to me.
 
AFA whether you got 40% or even 45% fill not likely to notice on inspection but if it looks like 60, 70 or 75% that would be noticeable and raise red flags for inspection and then get questioned on "how did you get that in the conduit?". The fill amount is not just about ease of pull but also heat dissipation. According to the Southwire app, you get with using copper 7 XHHW 500kcmill and one 1/0 EGC* fill @43.55%. Jam probability of 4.084142 very low. Not likely noticeable, but not compliant.

*using assumption related to 7 conductors parallel 500's and derated neutral @ 700A for a 1/0 EGC per table 250.122
 
Fred B said:
AFA whether you got 40% or even 45% fill not likely to notice on inspection but if it looks like 60, 70 or 75% that would be noticeable and raise red flags for inspection and then get questioned on "how did you get that in the conduit?". The fill amount is not just about ease of pull but also heat dissipation. According to the Southwire app, you get with using copper 7 XHHW 500kcmill and one 1/0 EGC* fill @43.55%. Jam probability of 4.084142 very low. Not likely noticeable, but not compliant.

*using assumption related to 7 conductors parallel 500's and derated neutral @ 700A for a 1/0 EGC per table 250.122
Click to expand...
I want to say neutral being considered is 4/0, so that is 6 500s, a 4/0, and a 1/0. Obviously if things are right right, that neutral won't have much contribution to heat load in the pipe, but certainly decreases the air volume, not that conduits really breathe much anyway.
 
fastline said:
I want to say neutral being considered is 4/0, so that is 6 500s, a 4/0, and a 1/0. Obviously if things are right right, that neutral won't have much contribution to heat load in the pipe, but certainly decreases the air volume, not that conduits really breathe much anyway.
Click to expand...
Southwire app shows this scenario at 40.30 % fill with XHHW, 40.18% with THHN. Only a slight space savings compared 7- 500's

Your option of using THHN 4- 750's and 1- 1/0 EGC you will come in at 36.95% fill and 3.362345 jam probability. Fill wise the better option. Cost savings between the 2 is very nominal particularly with the short run, around here only $2/ft less by running parallel vs the single.

Up here the winter weather would definitely play a role in choosing size as the larger wire is much harder to pull in the cold. Even 250's won't bend at 20 below.
 
You must log in or register to reply here.
Top